This application claims priority of European Application No. 01660097.5, filed May 17, 2001.
The invention relates to an adjusting mechanism for zonal control of an ink blade in respect of a ductor roller surface in a printing press having a frame, said adjusting mechanism comprising a plurality of moving means in contact with the ink blade and movable in a longitudinal direction towards and away from said ductor roller. The invention also relates to a method for zonal control of an ink layer thickness on a ductor roller by adjusting position of an ink blade in respect of a ductor roller surface in a printing press, in which method a plurality of moving means in contact with the ink blade are moved independently of each other in a longitudinal direction towards and away from said ductor roller.
Ink blades are used in ink supply units of printing presses, especially rotary printing presses like offset printing machines, together with a ductor roller or an ink fountain roller, for controlling the thickness of ink layer supplied to the actual printing roller, and so for controlling the amount of ink on the printing sheet. Publication EP-0 425 432 describes an ink blade, whose the free end section associated with the ductor roller comprises a plurality of slits or cuts, which are perpendicular to longitudinal direction of the free end, to create a zonal segmentation or tongues of the ink blade. Bending the each zonal segment individually towards the ductor roller and away from it alters the gap between the ductor roller and these zonal segments of the free end section. This bending is performed by adjusting mechanisms which are arranged side by side so that the head of the adjuster screw in each of said mechanisms are non-positively connected to one of the zonal segments. This kind of adjusting mechanism is disclosed in publication EP-0 425 432. The adjuster screw is provided with a zone screw passing through a crossbar, whereupon turning of the zone screw to one or the opposite direction displaces the head of the adjuster screw bending more or less the tongue of the ink blade. This type of variable bending alters the gap between the ductor roller and the tongue of the ink blade, and so affects the thickness of the ink layer on the ductor roller. The position of the head is indicated with a meter counting the turns of the zone screw. These kind of adjusting mechanisms using screws, gears, levers or the like have several drawbacks. Because at least some part(s) of the mechanism shall be moved in two directions opposite to each other the always inevitable backlash or slack back between the mechanical components causes an uncontrolled deviation from the ink layer thickness strived for. Further the size of the adjusting mechanism cannot in practise be miniaturized to whatever extent, and so the width of the tongues is limited to be 25 mm or greater. This lowest limit hampers reaching the best possible control of the ink layer thickness. The different bending ratio of the adjacent tongues of the ink blade creates lateral breaks in the free end section, whereupon streaks of ink are formed in the cut areas between the tongues extending along the periphery of the ductor roller, and causing streaks in the final print, too. Also the construction of this kind of adjusting mechanisms is complicated and requires high precision manufacturing methods, both of which causing higher production costs.
Publication DE-G-91 12 926 discloses an apparatus for zonal dosing of a fluid on a roller in a printing machine with dosing elements with a zonal breadth, which elements have supporting and dosing areas in direction of the roller axle, whereupon said supporting areas are continuously resting against the roller and whereupon said dosing areas of the dosing elements can be positioned at distances, which can be altered independently from each other. This is achieved by arranging the dosing areas of the dosing elements to consist of piezo-electric setting elements. There is no ink blade, but the piezo-electric elements are in direct contact with the roller surface. These piezo-electric elements does not control the amount of fluid fed onto the roller, but the piezo-electric elements operate to scrape afterwards the surplus fluid from the roller surface.
Publication DE-29 51 653 describes an apparatus for dosing a colorant onto the ductor roller in a printing machine, in which the amount of colorant applied in the coloring device is defined by a dosing strip, which can be zonally controlled by steering impulses and setting elements, whereupon each dosing zone of the dosing strip is provided with setting means, and these dosing zones are positioned with forms of impulses continuously during colorant feeding at the ductor roller, i.e. creating a determined gap, and whereupon the time of the stroke in each dosing zone is variable. The dosing strip includes several base plates placed side by side and movable in the direction of the ductor roller, and there is at least two slides movable in the direction of the ductor roller on each of the base plates, and each slide on the base plate is brought in groups alternately as a supporting element or as a dosing element for the ductor roller, and the single slides are operated by single drives acting on the slides. The publication does not describe the type of the drives, and the only active elements are ordinary helical springs. The dosing strips seem to be quite thick, and so very stiff, whereupon they cannot be driven against the ductor roller.
The object of the invention is to achieve an adjusting mechanism and a method for zonal control of an ink blade in respect of a ductor roller providing an accurate alteration of the gap between the roller surface and the edge of the ink blade, in which alteration movement the backlash should be as small as possible, or the alteration should be free from backlash. The second object of the invention is to achieve an adjusting mechanism enabling to minimize the widths for the tongues of the ink blade. A further object of the invention is to achieve an adjusting mechanism by which streaks of ink on the ductor roller can be avoided to a considerable extent. Still further object of the invention is to achieve an adjusting mechanism and a method enabling automation of said zonal control, though not necessarily a feedback regulation.
The above-described problems can be solved and the above-defined objects can be achieved by means of an adjusting mechanism and by means of a method as set forth by the invention. According to the first aspect of the inventive apparatus each of said moving means comprises: at least one bar of a shape memory material having a length at least partly in said longitudinal direction, a first end of the bar(s) being supported by said frame and a second end thereof adapted to said contact, and activating means positioned to provide a magnetic field strength or a temperature or an electrical voltage and current into said bar or bars; and said adjusting mechanism comprises: a control unit supplying a controlled electrical voltage/current into the activating means, whereupon the length of said bar is determined by the magnetic field strength or the temperature or the electrical voltage/current thereof. According to the second aspect of the inventive apparatus each of said moving means comprises: at least one bar of a shape memory material having a length at least partly in said longitudinal direction, and activating means positioned to provide a magnetic field strength or a temperature or an electrical voltage and current into said bar or bars; and said adjusting mechanism comprises: at least one force sensor to detect compression forces between said ink blade and said ductor roller, and a control unit supplying a controlled electrical voltage/current responsive to said compression forces into the activating means. According to the inventive method a higher or a lower electrical voltage/current and/or an inverse electrical voltage/current is provided into activating means for bar(s) of a shape memory material arranged within each of the moving means, whereupon a magnetic field strength or a temperature or a voltage/current in said bar is changed altering a dimension of said bar(s) thereby adjusting the position of the ink blade.
This invention describes a new principle of attaining small movement for the edge of the ink blade, or especially small movements for the edges of the ink blade segments. This new principle utilizes a bar of a Shape Memory Material (SMM) connected between the frame of the printing press and the edge area of the ink blade. In this context Shape Memory Material (SMM) intends any material having some kind of repeatability, i.e. memory, reached by any means. So the memory properties of SMM are not limited to any special type of transformation, but are based on some transformation in the material. Accordingly Shape Memory Material (SMM) may change its form or dimension because of transformation caused by change in temperature, or change in strength or direction of a magnetic field, or change in strength or direction of an electrical voltage or current. A material having only a volume change caused by the simple thermal expansion is not considered as a SMM, but Shape Memory Alloys (SMA) of any type, electrostrictive materials, magnetostrictive materials as well as piezoelectric materials are included the group of Shape Memory Materials (SMM). The main advantage of using SMM bars according to invention is that the length of the bar can be electrically or electronically controlled with high accuracy, whereupon a movement accuracy and repeatability of an order of 1 xcexcm for the edge of the ink blade can be reached. It is also possible to attain a movement of said edge without any noticeable backlash. Another advantage of using SMM bars according to invention is that the width of the blade segments can be reduced at least down to 12 mm. Further, utilizing the novel construction of the ink blade segments, it is possible to avoid the streaks of ink between the blade segments or tongues. All these features of the invention are effective in minimizing the size of the whole ink fountain in the printing press, and in minimizing the investment required.